The present invention relates to a friction stir welding method which is suitable for joining extruded frame members made of an aluminum alloy, such as are used in the manufacture of a railway vehicle or a building structure, for example.
Friction stir welding is a method in which, by rotating a round rod (called xe2x80x9ca rotary toolxe2x80x9d) which is inserted into a joint between the members being joined and moving the rotary tool along the line of the joint between the extruded frame members, the friction stir welding portion is heated, softened and plastically fluidized, and a solid joint is produced. The rotary tool is comprised of a small diameter portion which is inserted into the welding joint and a large diameter portion which is positioned outside of the small diameter portion of the rotary tool. The small diameter portion and the large diameter portion of the rotary tool have the same axis. A boundary between the small diameter portion and the large diameter portion of the rotary tool is inserted a little into the welding joint during welding. The above stated technique is disclosed, for example, in Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2).
As seen in FIG. 9 of Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2), the joining of two faces of hollow extruded frame members is carried out from one of the two faces of the hollow extruded frame member. Namely, the plates of one side face of each member are abutted, and from the other side of the other member, a friction stir welding is carried out on the abutted plates. The outer face sides of said plates are joined to provide a flat surface. An end portion of the plate of the other face side is orthogonal to the thickness direction. Further, as seen in FIG. 7 of Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2), by joining members each having a raised portion, a good friction stir welding is carried out.
As shown in FIG. 9 of the above stated Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2), a case where two plates (extruded frame members) having a long size, for example about 25 m, are abutted and are welded is taken into the consideration. During the welding, while the abutting portions of the plates are pressed down from above, the friction stir welding is carried out. The means for pressing is a pressing-down metal fitting means or a roller which moves together with the rotary tool. Further, after the two plates have been welded temporarily at spaced points with a predetermined pitch, by pressing down on the two frame members, the friction stir welding is carried out.
When the plates are long in size, there is a possibility that the end portion of the plate is deformed to have a waveform shape in the longitudinal direction (warp). In this case, as shown in FIG. 7 of the accompanying drawings, in the abutted portion, the ends of the two plates B1 and B2 will meet with a step-wise difference in an upper and lower direction. This step-wise difference can be removed by pressing down from above on the two members. However, to eliminate the step-wise difference, it is necessary to provide the pressing-down metal fixing means with a small pitch, with a result that the apparatus becomes high in cost.
Further, before the temporary welding and the friction stir welding can be carried out, it is necessary to eliminate the step-wise difference, or else there will be a problem. In this regard, when a step-wise difference remains after welding, it is impossible to remove the step-wise difference.
An object of the present invention is to abut plates to be welded in such a way that a step-wise difference does not exist at the welding joint when welding is carried out.
The above-stated object can be attained by a friction stir welding method comprising the steps of: inserting a projecting portion on an end of a plate of a first frame member into a recessed portion in an end of a plate of a second frame member to abut said frame members so as to form a welding joint; and inserting a rotary tool into the welding joint from one face of the members and carrying out friction stir welding of the other face of the members.
The above-stated object can be attained by a method of manufacturing a structural body comprising the steps of: inserting a projecting portion on an end of a plate of a first frame member into a recessed portion in an end of a plate of a second frame member to abut said frame members so as to form a welding joint; inserting a rotary tool into the welding joint from one face of the members and carrying out a friction stir welding of the other face of the members; and positioning a face of the one side of a structure which has been obtained by the friction stir welding as an outer face of a structural body for manufacturing the structural body.
The above-stated object can be attained by a method of manufacturing a car body comprising the steps of: inserting a projecting portion on an end of a plate of a first frame member into a recessed portion in an end of a plate of a second frame member to abut said frame members so as to form a welding joint; inserting a rotary tool into the welding joint from one face of the members and carrying out a friction stir welding of the other face of the members; and positioning a face of the one side of a structure which has been obtained by the friction stir welding as an outer face of a car body for manufacturing the car body.
The above-stated object can be attained by a friction stir welding of frame members wherein, a recessed portion is provided at an end face representing the thickness direction of a plate.
The above-stated object can be attained by a friction stir welding of frame members wherein, a projecting portion is provided at an end face representing the thickness direction of a plate.